A review of patents and literature on proposals and practices on converting wind energy into electrical energy are flawed for one or more of the following reasons:
1. Overestimating the energy of wind. The low density and viscosity of air develops only a small force per square inch. A large working area is required to develop an appreciable amount of force.
2. The low density and low viscosity makes airflow fragile and unstable. Extraneous structure and bends dissipate the wind energy.
3. The energy entering a converting device or apparatus can not be increased. The potential energy in an air stream is derived from the velocity head and the static head. Increasing the velocity of the air in venturi-type arrangements lowers the static head proportionately.
4. The air that has done its work must be removed. Structures that create turbulence downstream will block the removal.
5. Weather and climate must be a consideration to have wide application.
6. Failure to employ torque enhancing features.
7. Over-emphasizing omnidirectional capability.
8. Economics. Extravagant structure and intricate details add cost to fabrication and construction as well as to the maintenance costs.
The freestanding large diameter propeller-driven generator is the only type that has found application. The efficiency has been much exaggerated. The efficiency should reflect the percentage of the total wind available. This type of generator creates turbulence both laterally and downwind extending far beyond the working area of the propeller, which limits the closeness of the spacing between generators. Most of the wind available is wasted. The wide dispersal requires a large area of land. Another factor that lowers its efficiency is that the disk swept by the propeller is not uniformly loaded. A velocity profile diagram shows that the velocity is greater in the upper position than in the lower position. Thus the lower position is a drag on the upper. If the propeller is not oriented into the direction of the wind, the efficiency will decrease rapidly with shifts in the wind direction. Weather and climate limits the extent of its application because of the exposed design.